Drill construction

ABSTRACT

A spiral or twist drill having a hard metal cutting edge and particularly useful for drilling concrete or artificial stone includes a cutting edge having a centering projection of a diameter which is smaller than the outside diameter of the drill. The cutting edge is formed by a hard metal plate which is secured such as by soldering within a cross groove of the drilling head. The centering tip is formed either by a separate hardened metal element which projects outwardly from the center of the cutting plate or is defined by notches which are formed on each side of a central centering tip portion of the hard plate.

United States Patent Chrom y 1 July4,l972

[ 1 DRILL CONSTRUCTION 211 Appl. No: 26,677

2,673,714 3/1954 Hargrave ..175/410 1,007,037 10/1911 MacDonald ..175/389 2,230,645 2/1941 Jones ..77/70 2,646,701 7/1953 Letien ..77/70 3,460,409 8/1969 Stokey ..77/67 FOREIGN PATENTS OR APPLlC'ATlONS 584,358 10/1932 Germany ..175/410 Primary Examiner-James A. Leppink Attorney-McGlew and Toren [57] ABSTRACT A spiral or twist drill having a hard metal cutting edge and particularly useful for drilling concrete or artificial stone includes a cutting edge having a centering projection of a diameter which is smaller than the outside diameter of the drill. The cutting edge is formed by a hard metal plate which is secured such as by soldering within a cross groove of the drilling head. The centering tip is formed either by a separate hardened metal element which projects outwardly from the center of the cutting plate or is defined by notches which are formed on each side of a central centering tip portion of the hard plate.

6 Claims, 4 Drawing Figures PATENTEDJHL' 419. 2 3.674.101

INVENTOQ FQA NZ 66 0001) A TIDE/V65 DRILL CONSTRUCTION SUMMARY OF THE INVENTION This invention relates in general to the construction of drills and particularly to a new and useful drill particularly for drilling hard material such as concrete and artificial stone and which includes a hard metal cutting edge which presents a centering projection.

In the known spiral or twist drills with hard metal cutting edges for use in drilling concrete, artificial stones and similar materials, the cutting edge runs in a straight uninterrupted line from the tip of the drill to the outside diameter. When drilling concrete with a percussion drilling machine, such as an explosive charge driven device, if the drill impinges on a pebble with the cutting edge at a location outside of the tip there is a danger that drill tip will be diverted from the drilling center under the impact of firing unless there is also a pebble which is on the opposite side which deflects it backwardly into a center position. In drilling through the concrete this phenomenon recurs with every impact of the cutting edge on a pebble so that the drill tip is caused to travel around a theoretical drilling center. The result of this is that the drill produces a bore of triangular drill cross section rather than a round one. By the lateral diversion of the drill tip in the direction of the less compact material, the drill is pressed into an oblique position, that is, the drill slips. In order to avoid jamming of the drill, this oblique position cannot be corrected. This means that a bore curved in the longitudinal direction of the bore axis is formed and this renders the subsequent introduction of a spike difficult or even impossible.

In accordance with the present invention, there is provided a drill of the above mentioned kind which makes it possible to drill bores of round cross section and with a straight longitudinal axis. This is accomplished by employing a hard metal cutting edge which has a centering projection of a smaller diameter than the outside diameter thereof. With such a construction, when the drill impinges on a hard element, such as a pebble, with a portion thereof off center in respect to the tip; the centering projection will already have worked itself into the other material to an extent that the drill tip will no longer be diverted from the theoretical drilling center. The construction ensures that the travel of the drill tip around the theoretical drilling center will not occur and the drill will be driven in a straight line and not obliquely so that the resultant bore will he of round cross section and have a longitudinally straight axis into which a spike may be inserted without effort.

In one embodiment of the invention, the hard metal cutting edge presents at least one notch symmetrically arranged on each side of the drill center so that the centering projection is formed between the notches thus defined. With such a construction the ordinary hard metal plates which have been used up to the time of the present invention can be employed. By defining notches in the hard metal cutting edge it is no longer necessary to remove the entire drilling volume of material since the material in the zone of the notches will crumble away by itself. This results in a shortening of the drilling time or an increase in the drilling output.

Accordingly, it is an object of the invention to provide an improved drill construction which includes a cutting head having a hardened plate cutting member with a central projection which is less than the outside diameter of the drill.

A further object of the invention is to provide a cutting head for a drill which includes a diametrically arranged cutting plate having a centering tip formed centrally between two lateral notches defined in the end thereof.

A further object of the invention is to provide a drill construction which is simple in design, rugged in construction and economical to manufacture.

The various feature of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference'should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a partial side elevational view of a drill constructed in accordance with the invention;

FIG. la is a front elevational view of the drill indicated in FIG. 1;

FIG. 2 is a view similar to FIG. I of another embodiment of the invention; and

FIG. 3 is a view similar to FIG. I of still another embodiment of the invention.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings in particular, the invention embodied therein in FIGS. 1 and la comprises a drill I having a spirally extending drilling groove la defined therein and terminating in a head or end portion 4.

In accordance with the invention the head portion 4 is characterized by the provision of a hard metal plate 2 which, for example, is arranged to extend diametrically across the drill head in a transverse groove of the head and is secured in position, such as by soldering. The plate 2 includes a centering projection portion 3 which is pointed at the outer end to define a tip 3a which is centered along the axis of the drill. In the embodiment illustrated the drill I has a diameter D, for example, which is about PA inches; and the hard metal plate 2 is made slightly greater than this. The central projection 3 has a thickness of about one-fourth of an inch. The bevel angle of the centering projection is substantially the same as that of the hard plate 2 and it lies within the range of from 45 to 60.

In the embodiment illustrated in FIGS. 2, there is provided a drill 10 which includes a spiral drill groove 10a and a head portion 40 to which is secured a hard plate 20. The plate 20 includes notches l2 and I4 which are located in the cutting edge so as to define a centering tip 30 of a width which is comparable to that of the tip 3 in the embodiment of FIG. 1. The notches 12 and 14 also define drilling teeth 60 and 60' at respective opposite outer sides of the cutting edge. The notches I2 and I4 may advantageously be made to a depth in which they cut into a portion of the head 40.

In the embodiment of FIG. 3, there is provided a drill 10' which includes a head portion 40' having a plate 20' secured thereto. The plate 20' also includes a centering projection 30' which is defined between two notched areas 50 and 50' arranged on each side thereof. The construction forms the drilling teeth 60a and 60a of the rectangular configuration indicated.

In the known drills with hard metal cutting edges there was always the danger, when drilling through concrete, that the drill tip would be diverted from the theoretical drilling center when the cutting edge hits a pebble. With the drills constructed according to the invention, the danger is avoided first because the centering projection 3 or 30, or 30' works itself into the material. If then the following hard cutting metal edge impinges on the laterally aligned pebble, the centering projection which has already penetrated in the material will form the guide for the drill shank and prevent diversion of the drill tip by the hard metal cutting edge subsequently impinging on the pebble.

In the construction of the invention indicated in FIGS. 2 and 3, there is a further advantage in that the material between the centering projection 30 and 30' respectively and the drilling teeth associated therewith need not be removed by a cutting edge but the material will crumble away due to the blasting effect as the centering edges of the drill are driven in. Consequently the drilling output can be increased and hence the drilling time shortened.

What is claimed is:

l. A spiral or twist drill comprising an axially elongated drill having a shank portion with a spiral groove defined in the exterior surface thereof and terminating in a head, the head of said drill having a groove therein extending diametrically across and inwardly from its end, a flat planar hard metal plate positioned within said groove and securely attached to said drill, said plate having a pointed edge extending axially from said head of said drill with the point thereof located on the axis of said drill, said pointed edge comprising two surfaces each sloping from the point in a diametrically opposite direction toward the circumferential periphery of said drill, each said surface of said edge extending rectilinearly from the point to the circumferential periphery of said drill and each said surface having a notch formed therein through said plate from one side to the other, each notch spaced between and from the point and the circumferential periphery of said drill, said notches being symmetrically arranged relative to the axis of said drill, and the portion of said surfaces of said edge extending from said notches to the point of said edge forming a centering projection having a dimension in the diametrical girfiction of said drill which is less than the diameter of said 2. A drill, according to claim 1, wherein the notches are of curved configuration.

3. A drill, according to claim 1, wherein the notches are rectangular.

4. A drill, as set forth in claim 1, wherein said plate has a dimension in the diametrical direction of said drill which is slightly larger than the diameter of said drill so that said plate extends laterally from the head of said drill.

5. A drill as set forth in claim I, wherein said surfaces of said edge of said plate being disposed at a bevel angle in the range of 45 to 60.

6. A drill, as set forth in claim I, wherein said head of said drill being notched to form a continuation of said notch in said edge of said hard metal plate.

# it It i i 

1. A spiral or twist drill comprising an axially elongated drill having a shank portion with a spiral groove defined in the exterior surface thereof and terminating in a head, the head of said drill having a groove therein extending diametrically across and inwardly from its end, a flat planar hard metal plate positioned within said groove and securely attached to said drill, said plate having a pointed edge extending axially from said head of said drill with the point thereof located on the axis of said drill, said pointed edge comprising two surfaces each sloping from the point in a diametrically opposite direction toward the circumferential periphery of said drill, each said surface of said edge extending rectilinearly from the point to the circumferential periphery of said drill and each said surface having a notch formed therein through said plate from one side to the other, each notch spaced between and from the point and the circumferential periphery of said drill, said notches being symmetrically arranged relative to the axis of said drill, and the portion of said surfaces of said edge extending from said notches to the point of said edge forming a centering projection having a dimension in the diametrical direction of said drill which is less than the diameter of said drill.
 2. A drill, according to claim 1, wherein the notches are of curved configuration.
 3. A drill, according to claim 1, wherein the notches are rectangular.
 4. A drill, as set forth in claim 1, wherein said plate has a dimension in the diametrical direction of said drill which is slightly larger than the diameter of said drill so that said plate extends laterally from the head of said drill.
 5. A drill as set forth in claim 1, wherein said surfaces of said edge of said plate being disposed at a bevel angle in the range of 45* to 60*.
 6. A drill, as set forth in claim 1, wherein said head of said drill being notched to form a continuation of said notch in said edge of said hard metal plate. 